Implications of unique features of blood lipid transport in the lactating cow

Effects of Weaning Age on Plasma Biomarkers and Growth Performance in Simmental Calves

Weaning plays a key role in health status and future performance of calves. The aim of this study was to investigate the effects of weaning age (Wa), early (45 d, EW) or conventional (60 d, CW), on growth performance and metabolic profile of ten Simmental calves (5 EW and 5 CW calves). Daily intake of milk and calf starter was recorded. Blood samples and measurements of body weight (BW), heart girth (HG), and wither height (WH) were collected at −25, −15, 0, 6, and 20 days relative to weaning. Growth performances (BW, HG, WH) were affected by Wa, resulting lower in EW calves compared with CW calves (p < 0.05). Average daily gain was affected by overall Wa and Time but also by the interaction Wa × Time (p < 0.05). EW calves had lower paraoxonase and higher oxidation protein products levels, lower glucose levels in the post-weaning period, lower Ca and cholesterol levels at 20 d after weaning, and higher GGT activity at −25 d from weaning (p < 0.05). A significant interaction effect between Wa and Time was reached for glucose, Ca, cholesterol. In conclusion, weaning Simmental calves at approximately six weeks of age might not affect inflammatory status and liver functionality after weaning. As secondary outcome, even though the low number of animals could represent a limitation, the average daily gain obtained by Simmental calves weaned at 45 d supported this strategy (despite the lower body weight at weaning and after was due only to the age difference of 15 days). Hence, in order to reduce rearing costs, early weaning for Simmental calves (dual-purpose breed, milk and beef) might not jeopardize calf development, as long as calves can reach body gains as reported in the present study.

Effects of parity order on performance, metabolic, and hormonal parameters of grazing beef cows during pre-calving and lactation periods

Background

Metabolic profile evaluation is a tool widely used in ruminant nutrition as metabolic cues that relate nutrition to physiology. Metabolic and hormonal traits change during pre-partum and lactation according to parity in dairy cows, but studies of beef cows under grazing are scarce. The present study aimed to evaluate how metabolic and hormonal traits change over time, their relationship to performance, and determine if these factors differ according to the parity order of grazing beef cows. Thirty-six pregnant Nellore cows (12 nulliparous, 12 primiparous, and 12 multiparous) were used. The study started at 60 d prepartum until 203 d of lactation.

Results

The initial body weight (BW) and final BW were higher for multiparous cows (P > 0.05). An interaction occurred between parity and day (P < .0001) for body condition score. Nulliparous and primiparous body condition score were reduced from − 60 prepartum to 30 postpartum, then stabilized 60 postpartum (P < 0.05), while multiparous maintained body condition score from − 60 days until 60 days postpartum (P > 0.05). Calf BW, final BW, and average daily gain did not differ between parities (P > 0.05). Effect of day (P < 0.05) was detected for non-esterified fatty acids, triglycerides, total cholesterol, LDL, VLDL, progesterone, and insulin. An interaction was observed between parity and days for glucose, HDL, β-hydroxybutyrate, creatinine and IGF-1 (P < 0.05). Parity affected serum urea nitrogen, total proteins, albumin, and globulins (P < 0.05). Parity and day relative to calving did not impact total T3 and T4 (P > 0.05).

Conclusions

Hormonal and metabolic profile is strongly influenced by the stage of lactation. Time effects (pre-partum and lactation period) were more pronounced in nulliparous since they displayed more unbalanced metabolic and hormonal traits and lowered BCS pre- and postpartum.

Naked Mole-Rat, a Rodent with an Apolipoprotein A-I Dimer

A variety of rodents have been used as experimental animals in metabolic studies of plasma lipids and lipoproteins. These studies have included understanding the functional role of apolipoprotein A-I, the major protein on the surface of HDL. Reviewing the genomic database for entries for rodent apoA-I genes, it was discovered that the naked mole-rat (Heterocephalus glaber) gene encoded a protein with a cysteine at residue 28. Previously, two cases have been reported in which human heterozygotes had apoA-I with cysteine at residues 173 (apoA-I Milano) or at 151 (apoA-I Paris). Interestingly, both groups, in spite of having low levels of HDL and moderately elevated plasma triacylglycerols, had no evidence of cardiovascular disease. Moreover, the presence of the cysteine enabled the apoA-I to form both homodimers and heterodimers. Prior to this report, no other mammalian apoA-I has been found with a cysteine in its sequence. In addition, the encoded naked mole-rat protein had different amino acids at sites that were conserved in all other mammals. These differences resulted in naked mole-rat apoA-I having an unexpected neutral pI value, whereas other mammalian apoA-I have negative pI values. To verify these sequence differences and to determine if the N-terminal location of C28 precluded dimer formation, we conducted mass spectrometry analyses of apoA-I and other proteins associated with HDL. Consistent with the genomic data, our analyses confirmed the presence of C28 and the formation of a homodimer. Analysis of plasma lipids surprisingly revealed a profile similar to the human heterozygotes.

Performance, metabolic and hormonal responses of grazing Nellore cows to an energy-protein supplementation during the pre-partum phase

BACKGROUND

Supplementation programs for prepartum beef cows are usually adopted because the nutritional status of the cows upon calving is a main factor impacting reproductive performance of the next production cycle. This study evaluated the effects of 60-d pre-partum energy-protein supplementation on performance, metabolic and hormonal responses during the peripartum phase of grazing beef cows. Thirty-eight pregnant multiparous Nellore cows were assigned to a completely randomized design with two treatments: control (no supplement) and supplementation (1.5 kg of energy-protein per d with 30% crude protein, dry matter basis).

RESULTS

The supplemented cows had higher ADG pre-partum (P < 0.10), but postpartum ADG did not differ between treatments. Supplementation did not affect BCS and calf BW upon calving, on days 45 and 90, milk yield and composition (P > 0.10). No differences were found for forage intake and neutral detergent fiber digestibility (P > 0.10). The intake and digestibility of CP and OM increased in response to supplementation (P < 0.10). An interaction occurred between supplementation and peripartum days for BUN, βHB, T3 and T4, which had higher concentrations for supplemented cows at pre-partum period (P < 0.10). Concentration of others blood parameters significantly changed along peripartum days (P < 0.10). There was no difference in pregnancy rates and days from calving to conception between treatments (P > 0.10).

CONCLUSIONS

Providing an energy and protein supplement to grazing Nellore cows over the last 60 d of gestation improved their pre-partum energy balance. However, no post-partum carryover effects were detected.

Age-related metabolic changes of pre-weaned Simmental calves fed whole bulk milk and ad libitum calf starter

The present study aimed to investigate blood biomarkers encompassing the metabolic status of Simmental calves, with emphasis on weekly differences in the pre-weaning period. Ten Italian Simmental calves were used for the experiment and were offered 6 L of bulk whole milk/d from an open-bucket starting at day 2 from birth and through 5 weeks. Blood samples were collected at birth and weekly to assess biochemical indicators related to energy metabolism and liver function, minerals, markers of inflammation, and oxidative stress. Body weight (BW), heart girth (HG), and solid feed intake were positively affected by aging. Calves increased solid feed intake consumption after 2 week and reached a BW gain of 28.16 kg at 5 weeks. Most of blood biomarkers were affected by age, mostly concerned the period after birth and day 1, whereas no changes were observed for haptoglobin, urea, β-hydroxybutyrate, Na, and K. The amount of milk fed to calves throughout this study contributes to the maintenance of glucose concentration over time, coupled also with a considerable amount of starter intake. Glucose levels associated to the high ADG (0.89 ± 0.09 kg/d, mean ± SEM) suggest that calves experienced a positive energy balance throughout the entire pre-weaning period. Similar levels of haptoglobin and ceruloplasmin, together with a gradual increase of albumin, reflect good liver functionality and a stable condition regarding the inflammatory status. These results suggest that blood biomarkers of Simmental calves in the pre-weaning phase vary with growing stages.

Effect of raw soya bean particle size on productive performance and digestion of dairy cows

Differing soya bean particle sizes may affect productive performance and ruminal fermentation due to the level of fatty acid (FA) exposure of the cotyledon in soya bean grain and because the protein in small particles is more rapidly degraded than the protein in large particles, which influence ruminal fibre digestion and the amounts of ruminally undegradable nutrients. The objective of this experiment was to investigate the effects of raw soya bean particle size on productive performance, digestion and milk FA profile of dairy cows. Twelve Holstein cows were assigned to three 4 × 4 Latin squares with 21-day periods. At the start of the experiment, cows were 121 days in milk (DIM) and yielded 30.2 kg/day of milk. Cows were fed 4 diets: (i) control diet (CO), without raw soya bean; (ii) whole raw soya bean (WRS); (iii) cracked raw soya bean in Wiley mill 4-mm screen (CS4); and (iv) cracked raw soya bean in Wiley mill 2-mm screen (CS2). The inclusion of soya beans (whole or cracked) was 200 g/kg on dry matter (DM) basis and partially replaced ground corn and soya bean meal. Uncorrected milk yield and composition were not influenced by experimental diets; however, fat-corrected milk (FCM) decreased when cows were fed soya bean treatments. Soya bean diets increased the intake of ether extract (EE) and net energy of lactation (NEL ), and decreased the intake of DM and non-fibre carbohydrate (NFC). Ruminal propionate concentration was lower in cows fed WRS than cows fed CS2 or CS4. Cows fed cracked raw soya bean presented lower nitrogen in faeces than cows fed WRS. The milk of cows fed WRS, CS2 and CS4 presented higher unsaturated FA than cows fed CO. The addition of raw soya bean in cow diets, regardless of the particle size, did not impair uncorrected milk yield and nutrient digestion, and increased the concentration of unsaturated FA in milk. Cows fed cracked raw soya bean presented similar productive performance to cows fed whole raw soya bean.

Effect of the metabolic environment at key stages of follicle development in cattle: focus on steroid biosynthesis

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function, two different animal models were used. Experiment 1 compared Holstein-Friesian nonlactating heifers (n = 17) and lactating cows (n = 16) at three stages of preovulatory follicle development: 1) newly selected dominant follicle in the luteal phase (Selection), 2) follicular phase before the LH surge (Differentiation), and 3) preovulatory phase after the LH surge (Luteinization). Experiment 2 compared newly selected dominant follicles in the luteal phase in beef heifers fed a diet of 1.2 times maintenance (M, n = 8) or 0.4 M (n = 11). Lactating cows and 0.4 M beef heifers had higher concentrations of β-hydroxybutyrate, and lower concentrations of glucose, insulin, and IGF-I compared with dairy heifers and 1.2 M beef heifers, respectively. In lactating cows this altered metabolic environment was associated with reduced dominant follicle estradiol and progesterone synthesis during Differentiation and Luteinization, respectively, and in 0.4 M beef heifers with reduced dominant follicle estradiol synthesis. Using a combination of RNA sequencing, Ingenuity Pathway Analysis, and qRT-PCR validation, we identified several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, to be downregulated by the catabolic state. Based on this, we propose that the adverse metabolic environment caused by lactation or nutritional restriction decreases preovulatory follicle function mainly by affecting cholesterol transport into the mitochondria to initiate steroidogenesis.

Nutritional level and energetic source are determinants of elevated circulatory lipohydroperoxide concentration

Dietary energetic impact on oxidative stress is incompletely understood. Therefore, effects of diets on oxidative stress were studied using a crossover block design. In Expt 1, intake of metabolizable energy (ME) was restricted orad libitum. In Expt 2, isoenergetic and isonitrogenic diets were fed, replacing carbohydrate energy by energy of fatty acids. Circulatory lipohydroperoxides (LOOH), markers of acute oxidative stress, were expressed absolutely and in terms of cholesterol or TAG levels. In Expt 1, plasma (jugularis vein) LOOH was assayed in combination with whole-body oxidative metabolism using gas exchange and heart rate (HR) during feeding periods and at rest. In Expt 2, LOOH was assayed in plasma from portal and a large udder vein and a mesenteric artery. In Expt 1, intake increased VO2, HR and LOOH following overnight fast with higher values (P < 0·05) when feeding MEad libitum. Intake of MEad libitum(3 weeks) increased cardiac protein of cytochrome oxidase and endothelial-type nitric oxide synthase (P < 0·05), indicating adaptation of the heart to higher activity. Transient HR responses evoked by an antidiabetic drug (levcromakalim) revealed a linear positive correlation with relative LOOH (r20·79), supporting the relationship between oxidative metabolic rate and lipoperoxidation. Evidence for exogenous lipids as LOOH source provided the vessel-specific rise in LOOH through replacing carbohydrate ME by lipid ME (Expt 2). Thus, dietary energy level and energetic source are important for circulatory LOOH with a role of vascular activity in production of oxidant.

Plasma Paraoxonase, Health, Inflammatory Conditions, and Liver Function in Transition Dairy Cows

Paraoxonase (PON) is a liver protein with hydrolase activity that is released into the blood stream. Paraoxonase may serve as an index of liver function because it is drastically reduced in chronic liver damage. Sixty-seven periparturient dairy cows were used to evaluate the relationship between plasma PON, health problems, inflammatory conditions, and liver function. Baseline plasma PON concentrations during the first 30 d in milk (DIM) were retrospectively used to group cows into quartiles. Metabolic profile, lipid metabolites (e.g., nonesterified fatty acids, beta-hydroxybutyrate), inflammatory indices (haptoglobin, ceruloplasmin), low and high density lipoprotein cholesterol, vitamin A, vitamin E, reactive oxygen metabolites, total antioxidants, and PON in plasma were measured 2 wk before to 8 wk after calving. Weekly milk yield, body condition score, and all health problems were recorded. After parturition (7 DIM), cows in the lower PON group had the lowest plasma concentrations of negative acute phase proteins compared with the higher PON group for retinol binding protein (23.2 +/- 2.86 vs. 36.0 +/- 2.96 microg/dL of vitamin A), albumin (31.6 +/- 0.73 vs. 33.9 +/- 0.75 g/L), total cholesterol (2.04 +/- 0.30 vs. 2.45 +/- 0.42 mmol/L), and the highest concentrations of haptoglobin (0.67 vs. 0.24 +/- 0.03 g/L; positive acute phase protein) and globulins (37.2 vs. 32.3 +/- 1.4 g/L). Plasma bilirubin was highest in the cows (10.1 vs. 6.2 +/- 0.6 micromol/L) in the lowest PON quartile. Plasma PON was negatively correlated with haptoglobin (r = -0.39) and bilirubin (r = -0.42) and positively correlated with retinol binding protein (r = 0.54), albumin (r = 0.38), and cholesterol (r = 0.55) fractions. A total of 82.3% of cows in the lower quartile and no cows in the upper quartile experienced serious inflammation. Lower quartile cows produced 28.1 +/- 10.3 kg of milk/d; whereas upper quartile cows produced 38.3 +/- 7.7 kg of milk/d during the first 30 DIM. A reduction in the ability of the liver to cope with the increased metabolic demand near parturition in dairy cows can be diagnosed using changes in baseline plasma PON.

Metabolic changes in follicular fluid of the dominant follicle in high-yielding dairy cows early post partum

Characteristics of the intrafollicular environment to which the preovulatory oocyte is exposed may be one of the major factors determining subsequent fertility. The aim of our study was to examine to what extent metabolic changes that occur in early post partum high-yielding dairy cows are reflected in the follicular fluid (FF) of the dominant follicle (>8 mm). Nine blood samples were taken per cow from nine high-yielding dairy cows between 7 days before and 46 days after parturition. From Day 14 post partum on and together with blood sampling, FF samples of the largest follicle were collected from the same cows by means of transvaginal follicle aspiration. Serum and FF samples were analyzed using commercial clinical and photometric chemistry assays for glucose, beta-hydroxybutyrate (beta-OHB), urea, total protein (TP), triglycerides (TG), non-esterified fatty acids (NEFA) and total cholesterol (TC). All cows lost body condition during the experimental period (0.94+/-0.09 points) illustrating a negative energy balance during the experimental period. In FF, glucose concentrations were significantly higher and the TP, TG, NEFA and TC concentrations were significantly lower than in serum (P<0.05). The concentrations of glucose, beta-OHB, urea and TC in serum and in FF changed significantly over time (P<0.05). Throughout the study, changes of all metabolites in serum were reflected by similar changes in FF. Especially for glucose, beta-OHB and urea the correlations were remarkably high. The results from the present study confirm that the typical metabolic adaptations which can be found in serum of high-yielding dairy cows shortly post partum, are reflected in follicular fluid and, therefore, may affect the quality of both the oocyte and the granulosa cells.

Metabolite and ionic composition of follicular fluid from different-sized follicles and their relationship to serum concentrations in dairy cows

Metabolic changes in blood serum may be reflected in the biochemical composition of follicular fluid and could indirectly influence oocyte quality. The purpose of this study was to examine the biochemical composition of follicular fluid harvested from different-sized follicles and its relationship with that of blood serum in dairy cattle. Following slaughter, blood samples were collected from dairy cows n=30 and follicular fluid aspirated from three size classes of non-atretic follicles (<4 mm, 6-8 mm and >10 mm diameter). Samples remained independent between cows and between size classes within cows. Serum and follicular fluid samples were assayed using commercial clinical and photometric chemistry assays for ions (sodium, potassium and chloride) and metabolites (glucose, beta-hydroxybutyrate (beta-OHB), lactate, urea, total protein, triglycerides, non-esterified fatty acids (NEFA) and total cholesterol). Results showed that follicular fluid concentrations of glucose, beta-OHB and total cholesterol increased from small to large follicles and decreased for potassium, chloride, lactate, urea and triglycerides. There was a significant concentration gradient for all variables between their levels in serum and follicular fluid (P<0.05). Significant correlations were observed for chloride (r=0.40), glucose (r=0.56), beta-OHB (r=0.85), urea (r=0.95) and total protein (r=0.60) for all three follicle size classes and for triglycerides (r=0.43), NEFA (r=0.50) and total cholesterol (r=0.42) for large follicles (P<0.05). The results from the present study suggest that the oocyte and the granulosa cells of dairy cows grow and mature in a biochemical environment that changes from small to large follicles. Furthermore, the significant correlation between the composition of serum and follicular fluid for the above-mentioned metabolites suggests that metabolic changes in serum levels will be reflected in the follicular fluid and, therefore, may affect the quality of both the oocyte and the granulosa cells.

Separation of bovine plasma lipoproteins by a rapid ultracentrifugation method

The recently described method of centrifugation with iodixanol for the rapid separation of human plasma lipoproteins was adapted to separate bovine plasma lipoproteins. Density gradients were generated by mixing plasma with iodixanol 12% (w/v), followed by centrifugation at 350,000 g and 16 degrees C for 3 h 10 min in a vertical rotor. Gradients were unloaded dense-end first into 10 fractions. Human very low density lipoprotein (VLDL; density < 1.011 g/ml), low density lipoprotein (LDL; density = 1.016-1.039 g/ml) and high density lipoprotein (HDL; density = 1.039-1.090 g/ml) were resolved well at densities considerably lower than those traditionally reported in salt gradients. In gradients generated from 12% iodixanol, bovine LDL and HDL exhibited even lower densities (1.016-1.028 and 1.016-1.048 g/ml, respectively) with all lipoproteins occurring at the lower density region of the gradient. In contrast, density gradients generated from layers of equal volumes of 6% and 12% iodixanol readily separated bovine HDL from VLDL, whilst LDL still overlapped with HDL. The latter accounts for >80% of all bovine lipoproteins and exists as two populations, namely light and heavy HDL. Gradients generated from two layers of iodixanol recovered bovine HDL in five fractions. The hypercholesterolaemia associated with lactation resulted in a modest shift in the profile of HDL cholesterol towards lipoprotein particles of lower density (light HDL). Significant between-farm differences were also detected in the density profiles of bovine plasma cholesterol. This new method is suitable for use in research and diagnosis in relation to lipoprotein metabolism disorders in cows.

Time trends of plasma lipids and enzymes synthesizing hepatic triacylglycerol during postpartum development of fatty liver in dairy cows

We studied development of fatty liver in high producing dairy cows with free access to feed during the dry period and thus showed the combined effects of parturition and prepartum overfeeding. Postpartum liver triacylglycerol concentrations at 1 wk postpartum, as measured in liver biopsies, had increased more than 6-fold, which was preceded or accompanied by an increase in plasma NEFA concentrations. Concentrations of hepatic phospholipid changed only slightly. The amounts of total lipids in serum, very low density lipoproteins, and high density lipoproteins significantly decreased by .5 wk after parturition, and concentrations of high density lipoproteins rose steadily. The pattern was similar for concentrations of total cholesterol and phospholipid in serum. Total lipid concentrations in low density lipoproteins were not altered after parturition. The activity of microsomal phosphatidate phosphohydrolase in the liver showed a transient increase at .5 wk after calving, but activity of microsomal glycerolphosphate acyltransferase remained relatively constant. The activities of diacylglycerol acyltransferase had increased about twice at 1 wk after calving and remained at this high level until at least 4 wk after parturition. The rise in activity of diacyglycerol acyltransferase was probably a response to the extra influx of fatty acids to channel them into triacylglycerol. Activities of microsomal cholinephosphate cytidylyltransferase initially increased after calving and then decreased slightly. Activities of hepatic choline kinase had increased after calving. This study indicates that hepatic triacylglycerol accumulates because of the increased hepatic uptake of NEFA and the simultaneous increase in activity of diacylglycerol acyltransferase.

[The effect of the main protein source in rations of ewes and the time of blood collection on the glucose and triacylglycerol levels in blood at the beginning of lactation]

The effect of the protein source of the ration (soybean meal, cottonseed cake, corn gluten and fish meal) and the time (period) of blood sample taking was examined on the content of glucose and triacylglycerols in the blood during the initial lactation period. Thirty-six ewes of the Thessaloniki crossbred type were randomly allocated to 4 groups. The ewes of each group were fed ad libitum with one of the 4 different rations, respectively. From each ewe 4 blood samples were taken in different times. The experimental design was factorial 4x4 with 9 replicates with main factors the main protein source (ration), as well as the time of blood sample taking. The protein source effect on glucose and triacylglycerol concentration in blood was not significant, while that of time of blood sample taking was significant. The interaction "ration" X "time" of sampling for the glucose and TGC concentration was not significant.

Lipid absorption and transport in ruminants

The objective of this paper is to review new insights on the biological mechanisms of absorption and transport of lipid in ruminants, especially the modern concepts and analytical methods used in studies on structural properties and intravascular and tissue metabolism of lipoproteins and their factors of variation. The intestinal absorption of lipids (including long-chain fatty acids) is detailed, and variations in the qualitative and the quantitative aspects of absorption with diet composition, especially for high fat diets, are presented. Also, structural properties and distribution characteristics of lipoprotein classes in different lymphatic and blood vessels are compared across several animal species. Physicochemical and hydrodynamic properties of the lipoprotein particles and their apolipoprotein moieties are given for the main classes of lipoproteins. Finally, lipoprotein metabolism is discussed in relation to development and physiological, nutritional, and hormonal status. Intravascular metabolism of lipoproteins, including the role of lipolytic enzymes and lipid transfer proteins, is presented. Characteristics of the intestinal and hepatic synthesis of lipoproteins and apolipoprotein fractions are compared, especially through experiments stimulating the hepatic secretion of triglyceride-rich lipoproteins. Different methods of measurement of lipoprotein tissue uptake or secretion in ruminants are discussed.

Quantification of apolipoprotein A-1 in cow serum by single radial immunodiffusion

A single radial immunodiffusion assay was developed to determine the concentration of the major apolipoprotein A-I in bovine serum. Assay was performed using agarose gel plates with monospecific rabbit antiserum. Standards made with bovine high density lipoproteins or serum 10 times diluted were applied in 3-microliters amounts to each well in the gel. The assay working range was 2 to 22 mg of apolipoprotein A-I. The intraassay and interassay CV were 3.7 and 4.9%, respectively. Using protein A-I. The intraassay and interassay CY were 3.7 and 4.9%, respectively. Using radial immunodiffusion assay, 23 serum samples from cows at various stages of lactation were analyzed. Apolipoprotein A-I was significantly increased in midlactation compared with concentrations in early lactation or dry period.

High density lipoproteins from bovine plasma and follicular fluid do not possess a high affinity for glycosaminoglycans

Possible interactions between glycosaminoglycans and high density lipoproteins (HDL) in plasma and follicular fluid were examined. Total lipoproteins (d less than 1.21 g/ml) were obtained from plasma of five Holstein cows by ultracentrifugation and fractionated by gel filtration. Every other fraction from the HDL peak or fractions corresponding to the base and ascending portion of the HDL peak were composited and applied to a heparin-Sepharose affinity chromatography column. Elution profiles from both composites showed a peak that did not bind to the column that contained HDL devoid of apolipoprotein-E as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining and immunoblot analysis. Elution of lipoproteins from the ascending portion of the HDL peak resulted in a second minor peak eluting at 0.35 M NaCl, which was low density lipoprotein (LDL) contamination. Lipoproteins (d less than 1.21 g/ml) isolated from follicular fluid obtained from small, medium or large follicles also were subjected to heparin-Sepharose affinity chromatography. Two peaks were observed, one corresponding to the lipoprotein that did not bind to the column, the other eluted at 0.5 M NaCl and accounted for less than 2% of the protein applied. The second peak did not contain apolipoprotein-E or LDL. Bovine follicular fluid glycosaminoglycans (GAG) were isolated and subjected to HDL-Sepharose affinity chromatography. Less than 2% of the total GAG bound to the HDL column. Therefore, HDL in bovine specimens did not interact appreciably with heparin or GAG isolated from follicular fluid.

Mammary blood flow and regulation of substrate supply for milk synthesis

In ruminants, mammary supply of substrate varies with rate of mammary blood flow and concentrations of blood substrates. Blood concentrations of most mammary substrates, except acetate and tryptophan, do not vary greatly with feed intake, short term. Fasting reduces mammary blood flow, whereas milking and injection of growth hormone or thyroxine increase flow. It is proposed that the fraction of cardiac output that perfuses the udder of lactating ruminants plays a role in regulation of nutrient partitioning between milk and body tissues. In fed animals this fraction is 15 to 16% of cardiac output, which declines on fasting to 8 to 9% and increases slightly following growth hormone treatment to 17.6%. Following realimentation of fasted cows or goats, mammary blood flow takes several hours to return to normal. Investigation of the mechanism of this response, in terms of the ability of the animal to recognize its nutritional status and partition nutrients accordingly, should prove fruitful to understanding causes of variations of milk production in response to feed quantity and quality. Several substrates show increased mammary arteriovenous difference with increasing blood concentrations. This may reflect differing ratios of blood flow:milk yield. The steep gradient of concentration of substrates across the mammary epithelial cell membrane suggests that a major impediment to substrate supply for milk synthesis is the rate of substrate transport across the membrane.

Effect of dietary fat supplement on lipid metabolism of Holstein Heifers

Twenty Holstein heifers were fed four rations containing 0, 10, 20, and 30% whole sunflower seed as a source of dietary fat. All rations consisted of alfalfa hay, sunflower hulls, and grain mixtures and were isonitrogenous at 12% crude protein and isocaloric at 2.6 Mcal metabolizable energy per kilogram dry matter. Average body weight gains were not different among treatment groups. Heifers fed sunflower seed (fat) diets consumed less total dry matter, significantly improving growth efficiency (gain/feed). Concentration of total lipid and urea nitrogen in blood serum were increased whereas glucose was depressed with higher amounts of dietary fat. High fat diets (20 and 30%) elevated total lipid, triglyceride, and nonesterified fatty acids in the blood. Total and free cholesterol in blood also were increased, but high density lipoprotein-cholesterol remained unchanged with increasing concentration of dietary fat. Dietary fat was correlated positively with lipid components of blood serum and negatively with glucose.

Isolation and characterization of lipoprotein lipase activators from bovine blood serum

Bovine serum lipoproteins were fractionated into high density and low and very low density lipoproteins by precipitation with sodium phosphotungstate and magnesium chloride. From each lipoprotein fraction seven apo C peptides were isolated by gel filtration and ion exchange chromatography. The two lipoprotein fractions probably contain identical apo C peptides but in different proportions. Two of the apo C peptides activated lipoprotein lipase from milk in vitro. Their specific activities were about 2000 times as high as that of the original serum. The apo C fraction from low-very low density lipoproteins had a specific activity three times that from high density lipoproteins. Also, the activator peptides from low and very low density lipoproteins gave one band on alkaline urea gel electrophoresis whereas corresponding peptides from high density lipoproteins were slightly heterogeneous. The low and very low density lipoproteins, therefore, seem to be the fraction of choice for isolation of activators for lipoprotein lipase.

Fractionation of plasma triglyceride-rich lipoproteins of the dairy cow: evidence of chylomicron-size particles

Electron micrographs of bovine triglyceride-rich lipoproteins demonstrated spherical particles with diameters up to 3000 A. Chylomicron-size particles (larger than 750 A) were isolated specifically by rate zonal centrifugation. Subfractionation by rate zonal centrifugation, isopycnic centrifugation, and gel filtration chromatography all indicated a wide range of bovine triglyceride-rich lipoproteins from chylomicrons to very low density lipoproteins. Chemical analysis of subfractions from gel filtration showed changes in the ratio of triglyceride/protein characteristic of chylomicrons versus very low density lipoproteins. Electrophoretic analysis on agarose gels of bovine chylomicrons obtained by centrifugation and gel filtration showed migrating bands similar to very low density lipoproteins, unlike human chylomicrons. Evidence of bovine chylomicrons provides support for the concept of a significant contribution to milk fat from intestinally absorbed lipid in the dairy cow.

Lipotropic effect of estradiol-17 beta in fed and fasted lactating cows

The lipotropic effect of estradiol-17 beta was measured in seven nonpregnant Holstein-Friesian cows 2 to 5 wk into lactation. The experiment was divided into an initial 3-day control period, 19 days treatment, and 2 days fast. Jugular blood samples were taken twice daily during the control period, the last 2 days of treatment, and the fast. After the control period, four cows received daily injections of estradiol-17 beta benzoate (15 mg) in sesame oil for the remainder of the experiment whereas three cows received injections of sesame oil only. Estradiol-17 beta did not change triglyceride concentration of plasma during the treatment period but increased it markedly during fast. Estradiol-17 beta increased the free glycerol concentration of plasma during treatment. Cholesterol concentrations of plasma showed a consistent trend lower in the estradiol group during treatment and fast. No differences were apparent in glucose and blood ketone concentrations. The concentration of insulin in plasma was lower for the estradiol group during treatment. Estradiol-17 beta appears to have a similar effect on lipid metabolism in dairy cows to other species. However, it exerted a strong lipotropic effect only under fasting.

Serum low density lipoproteins with mitogenic effect on cultured aortic smooth muscle cells

Low density lipoprotein (LDL) subspecies of different size and lipid mass were isolated by density gradient ultracentrifugation from the serum of male rhesus monkeys (Macaca mulatta) fed both a low fat, low cholesterol commercial primate ration, and cholesterol-supplemented high-fat diets, as well as from the serum of human donors. The mitogenic effect of these lipoproteins was examined using primary cultures of rhesus aortic smooth muscle cells. It was observed that the smaller LDL (molecular weight 2.7 X 10(6) from normolipidemic monkeys and a small LDL (molecular weight 2.6 X 10(6) occurring in some normal human subjects exhibited no mitogenic action. In turn, the larger LDL subspecies (molecular weight greater than 3.0 X 10(6), and buoyant density less than 1.030 g/ml), whether from normolipidemic or hyperlipidemic monkeys, or from some normal human subjects, had a marked proliferative action. The results indicate that both hyperlipidemic and normal sera (both human and rhesus) contain mitogenic LDL species although in different amounts. LDL-III, the rhesus equivalent of human Lp(a) was not mitogenic despite its similarity on size and lipid composition to the stimulating particles. However, on the removal of most of its large sialic acid moiety, a clear mitogenic action was observed. The mechanisms responsible for the proliferative effect are unclear and may involve LDL mass, lipid composition, and surface charge although other speculations cannot at present be ruled out. Furthermore, since the small LDL subspecies of either rhesus or human origin were nonmitogenic and similar in mass to the LDL found in calf serum, the mitogenic response of the smooth muscle cells to large LDLs may depend on their early conditioning with the LDL of calf serum.

Post-heparin lipolytic activity with no hepatic triacylglycerol lipase involved in a mammalian species

It was found that lipolytic activity in bovine post-heparin plasma differed from that of other mammalian species by the fact that intravenous heparin induced the release of lipoprotein lipase but not hepatic triacylglycerol lipase. Initially, this fact was strongly suspected when no remaining lipolytic activity could be found after whole bovine post-heparin plasma had been tested with either 1 M NaCl or antiserum against lipoprotein lipase. This was further confirmed by using heparin-Sepharose affinity chromatography when the entire lipolytic activity was eluted with 1.5 M NaCl but none with 0.4 or 0.7 M NaCl. The active fraction had lipoprotein lipase characteristics, i.e. it required serum activators to produce optimum activity and was fully inhibited by NaCl of high molarity and by anti-lipoprotein lipase antiserum. Neither the different doses of heparin nor the various times of sampling altered the results. This raises the question whether hepatic triacylglycerol lipase is absent from the bovine liver or whether this enzyme is present but cannot be released by heparin.

Fat in lactation rations: review

Recent research has demonstrated the effectiveness of added fat in diets to maintain milk production and fat percent. Much of the earlier work which indicated that fat affects digestion negatively may not be applicable because of great differences in the nature of diets and fats fed and especially in total feed intake. Nevertheless, much remains to be learned about interactions of fat, fiber, calcium, and rumen microorganisms if feeding of fat is to be maximized. The uniquely high acidity in the duodenum combined with detergent action of bile acids, lysolecithin, and fatty acids causes saturated fatty acids to be more digestible in ruminants than in nonruminants. Large quantities of added dietary fat increase concentrations in plasma of very low density lipoprotein triglyceride which increases their uptake by the mammary gland with inhibition of short chain fatty acid synthesis and consequent changes in milk fatty acid composition. In some cases, secretion of milk fat is increased. Current research and practice demonstrate that 3 to 5% fat may be added to diets for lactation to increase energy intake of high-producing cows and/or to reduce starch feeding, thereby increasing the ratio of forage to concentrate to prevent depression of milk fat.